<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    div{
        
        margin: 0;
        padding: 0;
        height: 550px;
        width: 550px;
        display: flex;
        justify-content: center;
        align-items: center;
        background: linear-gradient(125deg,red,orange,green,blue);
        background-size: 300%;
    }

</style>

<body>
    <div></div>
    
</body>
</html>